Engine fuel system



Jan. 24, 1956 E. ORENT ETAL 2,731,976

' ENGINE FUEL SYSTEM Filed April 26, 1951 2 Sheets-Sheet 1 (Ittornegs Jan. 24, 1956 E. ORENT ET AL 2,731,976

ENGINE FUEL SYSTEM Filed April 26, 1951 zsneets-sheet 2 Jul {a y I; 3%

I (Ittornegs United States Patent ENGINE FUEL SYSTEM Edward Orent and Stuart F. Kutsche, Grand Rapids,

Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 26, 1951, Serial No. 223,060 14 Claims. (Cl. 137-118) This invention relates to fluid distribution systems, particularly to fuel distribution systems for gas turbine aircraft engines.

Such engines ordinarily include a number of more or less independent combustion chambers, each with a liquid fuel spray tuozzle or equivalent fuel injection means, or a single combustion chamber fitted with a number of fuel nozzles.

Both to obtain most efficient operation and to minimize the possibility of damage to the engine, it is important that each nozzle delivers the same amount of fuel. Moreover, under extreme altitude conditions, even a slight variation in fuel delivery of an individual nozzle from that desired may result in extinction of the flame or overheating of the combustion chamber.

The problem of maintaining equal delivery from all nozzles is complicated by the wide range of fuel consumption of an aircraft gas turbine, which may vary over a range of thirty to one between sea level maximum power operation and high altitude cruising operation.

With a fixed nozzle, a flow range of thirty to one requires a pressure range of nine hundred to one. Such a range is impracticable, as effective atomization cannot be obtained at the low-pressure end of such a range.

This fact has led to various proposals, such as returning fuel from the nozzles to the supply; nozzles in which the number or area of fuel ports is varied; and nozzles with two sets of swirl p'orts. None of'these' attacks on the problem has led to entirely satisfactory results. a

Dual nozzles with two sets of swirl ports of different area, including a valve in each nozzle to close the large ports until the pressure at the small ports reaches a value indicating a rate of flow sufficient to secure adequate atomization from flow through the large ports, have probably been the most successful and least complicated of all the proposed systems.

With these,'however, it is 'a practical impossibility to equalize the valves in all the' nozzles so as to initiate flow to the large swirl ports of all the nozzles simultaneously. There is thus a range offuel flow within which maldistribution of fuel results from the fact that the large'ports of only some of the nozzles are open, or the valves in the nozzles unequally throttle flow to the several nozzles. This difliculty does not arise at high or low flows, but is acute in the middle range.

Moreover, the valves may jam or stick because of in the fuel. 7

At least two other causes of uneven distribution exist. One is the variation between individual nozzles. This can be minimized by careful manufacture, maintenance, and testing. The other is the variation in hydrostatic head between nozzles located at different elevations on the engine. This effect is material only at very low fuel pressures corresponding to low flow values, but may be troublesome then.

, 2,731,975 Patented Jan. 24, 1956 In addition, poor manifolding or unequal resistance to flow in supply lines to the nozzles will create unbalance.

This invention is directed to a system which retains the advantages of the dual fuel nozzle while eliminating or greatly reducing the disadvantages thereof.

/ In brief outline, the system of the invention involves the provision of a single flow divider to divide flow between the small and large flow ports or nozzles. This eliminates the individual valves at the nozzles and the troubles arising therefrom. The system also provides a flow divider which concurrently throttles the flow to the large nozzles or ports when these are in operation, thus correcting in large measure flow variations due to differences in the characteristics and locations of the nozzles. By virture of the inherent characteristics of dual nozzles, which are suited to a wide range of flows, the system is highly suitable for such a range. Moreover, the system is simple and substantially trouble-proof.

The principal objects of the invention are to improve the operating characteristics of gas turbine aircraft engines, to provide an improved fuel distribution system from such engines, and to provide an improved flow distributor.

Other objects of the invention, the advantages there'- of, and the manner in which these are realized, will be more fully apparent to those skilled in the art from the succeeding'description of preferred embodiments of the invention.

Referring to the drawings, Figure 1 is a schematic diagram of a gas turbine fuel distribution system; Fig ure 2 is a longitudinal section of a fiow divider in accordance with the invention; Figure 3 is a transverse section thereof taken on the plane indicated in Figure 2; Figure 4 is a fragmentary elevation view; Figure 5 is a longitudinal section of a modified flow divider; and Figure 6 is a fragmentary sectional view of a still further modified flowdivider incorporating features of the other two forms.

In Figure 1, six combustion chambers of an aircraft gas turbine engine are indicated at 11. The engine is not further illustrated, as the structure of the engine as such is immaterial to the invention, and is generally understood.

Fuel may be supplied in conventional manner from a fuel line 12 by a pump 13 and a fuel regulator 14 which by-passes some of the fuel through a line 16 to-the pump inlet. The regulator may be controlled by a lever 17. The metered fuel is supplied through a line 18 to the flow divider unit 20.

Each combustion chamber 11 is fitted with a small flow fuel inlet 21 and a large flow fuel inlet 22. These inlets may communicate with individual small and large nozzles, or preferably with small and large swirl ports in a duplexfuel nozzle for each chamber. Such nozzles are well known and are not illustrated, as the invention is not concerned with the details of the fuel nozzles or other injection means. It will be understood that valves in the nozzles are not required. It will also be understood that'all the injectors supplied by the inlets 21 and 22 might be in a single combustion chamber.

The small flow inlets 21 may be supplied from a ring manifold 23, which may encircle the engine, and is illustrated schematically in Figure I as being supplied from the flow divider 20 through parallel fuel lines 24. Each of the large flow inlets 22 is supplied through a separate fuel line 26 from the fiow divider 20.

The lines 24 are continuously connected to the line 18, and receive all the output from the fuel regulator 14 until the flow reaches a predetermined value. At this point, a metering piston in the flow divider begins to open metering ports communicating with the lines 26,

3 hich por s ope pr gressively as the total flow increases.

The flow divider 20 (Figures 2, 3, and 4) comprises a body 27, which, with sleeves 28 and 29 therein, defines a cylinder Within which a piston or plunger 31 may reciprocate.

The sleeve 28 is piloted within the sleeve 29 as indicated at 32, and the two sleeves are brazed together. Before .the sleeves are assembled the lower sleeve is ground to a high degree of precision to provide a number of identical -shaped slots 33 with the apices down. these slots defining, with the lower edge of the sleeve 28, a number of metering ports. The body 27 is drilled and tapped to provide an outlet 3.4 communicating with each metering port, to which a fuel line 26 may be connected.

The divider .as illustrated has ten metering slots and ten corresponding outlets, such as outlets 34, two of which are offset above the plane of Figure 3. Outlets in excess of the number required may be closed by plugs 36.

An inlet head 37 and an outlet head 38 are fixed to the body 27 by cap screws 39 or the like, which may extend through the parts 37 and 27 into the outlet head, which is tapped to receive them. Gaskets 41 are fitted between these parts. An extension 42 of the inlet head defines a fuel inlet 43, to which a fuel line such as line 18 may be secured by means of studs 44.

The piston 31 is provided with projections 46 on its lower face which bottom against the cylinder head '37. It is tapped for a threaded plug 47 which is bored to define a restricted orifice 48. The piston is biased toward the inlet end of the cylinder by a coil spring 49 which also engages a collar 51. The collar 51 is biased against a shoulder 52 in the sleeve 28 by a coil spring 53. The spring 53 is retained by an adjustable retainer 54 threaded into the outlet head. The retainer is formed with a hexagonal hole 56 which permits fuel flow and provides for adjustment of the retainer. The retainer is locked in place by an annular plug 57. The retainer 54 and plug 57 may be adjusted through an opening 58 in the outlet head 38.

While the opening 58 might be closed in any desired manner, the flow dividers illustrated are adapted for mounting on a flange of a fuel nozzle to supply directly the small and large fiow inlets 21 and 22 of one combust-ion chamber.

As illustrated in Figure 5, which shows a flow divider generally similar to that of Figure 2, the upper body 38 or 38a is provided with a groove for an O-ring 59, and may be bolted or otherwise secured to the flange 61 of a fuel nozzle body 60. The small flow inlet 21 of the nozzle 60 is aligned with, and supplied by, the passage 58.

To supply the large flow inlet of the nozzle 60 on which the flow divider is mounted, aligned passages 62 and 63 (Figure in the body parts 27a and 38a, corresponding to the parts 27 and 38 of Figure 2, connect one large flow outlet to the nozzle inlet 22. The direct outlet of the passage 34 is closed by a plug 36.

It is unnecessary to show any further structure of the nozzle 60, as it may be of any suitable duplex type.

The outlet head 38 or 38a is cross-drilled to form a passage 65 intersecting the passage 58, the ends of which are tapered to provide two outlets for the fuel to the additional small flow nozzles. These outlets are illustrated in Figure l as connected to lines 24. However, the manifold 23 may be directly connected to these outlets, as indicated in Figure 2.

Referring specifically to Figure 2, the spring 53 is considerably heavier than the spring 49. Therefore, when pressure is exerted on the piston 31, it compresses the spring" 49 rather than the spring 53 until the piston engages the collar 51. This engagement occurs just before the piston begins to open the ports 33. Further movement is opposed by the spring 53. The maximum opening of the ports is limited by engagement of the collar 51 with the head 38. Preferably, the areas of the ports under this condition are small enough to provide a substantial pressure drop across the ports to aid in equalizing flow to the nozzles even under maximum flow conditions.

The operation of the flow divider is as follows: Fuel is introduced from the regulator through line 18 and inlet 43. For small flows, the ports 33 are closed, and all the fuel flows through the orifice 48, retainer 54, ring 57, and outlets 58 and to the small flow inlets of nozzles 21.

The pressure ahead of the restriction 48 is exerted on the under side of piston 31, and the pressure behind the restriction on the upper side of the piston. As flow increases, the pressure differential increases, and begins to compress the spring 49.

The preliminary movement of the piston serves to free it from. any dirt which might tend to cause the piston to stick in the cylinder, without opposition from the metering spring 53.

The pressure differential on the piston 31 depends upon flow and is independent of the absolute pressure in the line. When the pressure differential reaches a predetermined point indicating sufficient flow to initiate operation of the large flow nozzles, the resultant force begins to lift the piston against the force of the metering spring and open the ports 33. Thus the flow is divided between the two sets of nozzles and between the nozzles of the large flow set.

Since the resistance to flow at the ports 33 is in series with the resistance at the nozzles, it tends to equalize flow notwithstanding differences in flow resistance or static head in the nozzles or the lines thereto. The effect is most pronounced at relatively low flows When the ports 33 are only slightly open.

The tapered or V-shaped form of the ports makes the apparatus more sensitive when the flow is not large. The piston 31 readily responds to variations in fiow. Once the ports 33 begin to open, the flow to the small nozzle ports increases only slightly, the actual increase depending upon the variation in force exerted by the spring 53 over its range of flow-throttling movement.

The proportions of the apparatus will, of course, be adapted to the installation requirements according to known principles of design of hydraulic equipment. The characteristics of a given flow divider may be readily adjusted within limits by varying the setting of the spring 53. Further variation may be made by substituting plugs 47 with metering orifices of different size, or springs 53 of different characteristics.

The modified form of flow divider shown in Figure 5 performs the same functions as the form previously described, and the structure of the housing, including inlet and outlet arrangements, may be the same. One ditference lies in the elimination of the collar 51 and auxiliary spring 49 of Figure 2. A further feature illustrated in Figure 5 is a pressure takeoti connection for instrumentation or control purposes. As will become apparent, this could be incorporated also in the structure of Figure 2.

The body parts 37a, 27a, and 38a of Figure 5 are similar to the corresponding parts of Figure 2, except as will be noted. O-rings 67 are shown as an alternative to the gaskets 41 of Figure 2.

The collar 51 is eliminated, and the metering spring 53 acts directly on the metering piston 31a through an annular spring seat 68, a spherical surface of which engages in a spherical socket in the orifice plug 47a fitted in the piston 31a. This plug is formed with the orifice 48, as previously described.

The piston 31a reciprocates in a sleeve composed of two sections 28a and 29a, the latter being ground to define V-shaped metering orifices 33a. These orifices are relieved behind a narrow lip 33b, thus providing a thin-edged orifice which facilitates precise grinding of the orifices.

So far as flow division is concerned, the device of 5 Figure 5 operates in the manner previously described, except that the'pretravel of the piston 31abefore' the metering ports open must be effected against the resistance of the spring 53.

The pressure takeoff arrangement comprises a circumferential groove 71 in the plunger 31a which is in communication with pressure downstream from the orifice 48 through radial ports 72 in theplunger. The groove 71 registers in all positions of the plunger with radial passages 73 in' the sleeve 28a which connect through a groove 74 in the sleeve with a drilled passage 76 in the body 27a communicating with a tapered opening 77 for a pipe such as 78.

The pressure takeoff connection 78 may take the place of an outlet 34 in the body. 4 z

This arrangement provides a highly desirable means for taking off, for information or control purposes, the value of the static pressure of the fuel fed to the small flow inlets.

It will be apparent that the collar 51 and pretravel spring 49 of Figure 2 could be incorporated in the flow divider of Figure 5 if desired, and would not disturb the operation of the pressure takeoff.

This is illustrated in the fragmentary view of Figure 6 in which parts previously described with: reference to Figures 2 and 5 retain the numbers applied to them in those views. The sleeve 28b, 29b is like sleeve 28a, 29a except that it provides a ledge or abutment 52 for the collar 51. Collar 51 is urged downwardly by the heavy spring 53 and the relatively light spring 49 is mounted between the flange of the collar 51 and the bottom of piston 31b. Piston 31b embodies the static pressure opening 72 which connects with the static pressure passage 76 in the body as in Figure 5. The piston 31b is otherwise like the piston 31 of Figure 2 and has mounted therein the orifice plug 47 which serves as a pilot for the collar 51.

The advantages of the invention will be apparent to those skilled in the art from the foregoing. Many modifications of the illustrative embodiments may be devised by the exercise of skill in the art, and the invention is not to be considered as limited by the detailed description of these embodiments.

We claim:

1. A flow divider comprising, in combination, a cylinder, a pistol freely reciprocable therein and provided with a constant-area restricted fluid passage between the faces thereof, a fluid inlet at one end of the cylinder, a first fluid outlet at the other end of the cylinder, resilient means biasing the piston toward the inlet end of the cyinder, and a fluid metering port formed in the wall of the cylinder, the metering port being connected to a second fluid outlet, the port being located so as to be closed by the piston in its normal biased position at the inlet end of the cylinder and to be opened by the piston by I movement of the piston from the normal position, the said restricted fluid passage being the sole outlet for fluid entering the inlet when the piston is in the said normal position.

2. A flow divider comprising, in combination, a cylinder, a piston freely reciprocable therein and provided with a constantly open restricted fluid passage between the faces thereof, a fluid inlet at one end of the cylinder, at first fluid outlet at the other end of the cylinder supplied through the said passage, resilient means biasing the piston toward the inlet end of the cylinder, and a plurality of fluid metering ports formed in the wall of the cylinder, each metering port being connected to a distinct fluid outlet, the ports being located so as to be closed by the piston in its normal biased position at the inlet end of the cylinder and to be opened concurrently by the piston by movement of the piston from the normal position.

3. A flow divider comprising, in combination, a cylinder, a piston freely reciprocable therein and provided with a restricted fluid passage between the faces thereof,

a fluid inlet at one end of the cylinder, a first fluid outlet at the other end of the cylinder, resilient means biasing the piston toward the inlet end of the cylinder, and a fluid metering port formed in the wall of the] cylinder, the metering port being connected to a second fluid outlet, the port being located so as to be closed by the piston in its normal biased position at the inlet end of the cylinder and to be opened by the piston after an initial range of idle movement from the normal position} the resilient means comprising a first means offering relatively light resistance to movement of the piston at least through a substantial part of the idle range and a second means offering relatively heavy resistance effective through at least part of the movement of the piston over the range of opening of the metering port.

4. A flow divider comprising, in combination, a cylinder. a piston freely reciprocable therein and provided with a restricted fluid passage between the facesthereof, a fluid inlet at one end of the cylinder, a first fluid, outlet at the other end-of the cylinder, resilient means biasing the piston toward the inlet end of the cylinder, and a plurality of fluid metering ports formed in the wall of ,the cylinder, each metering port being connected to a distinct fluid outlet, the ports being located so as to befclosed by the piston in its normal biased position at the inlet end of the cylinder and to be opened concurrentlyby the piston after an initial range of idle movement from the normal position; the resilient means comprisinga first means offering relatively light resistance to movement of the piston through a substantial part of the idle range and a second means offering relatively heavy resistance to further movement of the piston effective through at least part of themovement of the piston over the range of opening of the metering ports.

5. A flow divider for a gas turbine fuel system or the like comprising, in combination, a body defining a cylinder, means defining a fluid inlet at one end of the cylinder, means defining a fluid outlet at the other end of the cylinder, a piston reciprocable in the cylinder formed with'a restricted opening therein for flow of fluid from the inlet to the outlet, means, biasing the piston toward the inlet end of the cylinder, means defining a plurality of metering ports in the wall of the cylinder adapted to be concurrently and progressively opened by'the piston by movement thereof away from the inlet end of the cylinder, 21 set of fluid discharge connections in the body, duct means connecting each said port to a said discharge connection, and a static pressure connection extending from the cylinder at the outlet side of the piston, to an external connection on the body.

6. A flow divider for a gas turbine fuel system or the like comprising, in combination, a body defining a cylinder, means defining a fluid inlet at one end of the cylinder, means defining a fluid outlet at the other end of the cylinder, a piston reciprocable in the cylinder formed with a restricted opening therein for flow of fluid from the inlet to the outlet, means biasing the piston toward the inlet end of the cylinder, means defining a plurality of metering ports in the wall of the cylinder adapted to be concurrently and progressively opened by the piston by movementthereof away from the inlet end of the cylinder, a set of fluid discharge connections in the body, and duct means connecting each said port to a said discharge connectlon.

7. A flow divider for a gas turbine fuel system or the like comprising, in combination, a body defining a cylinder, means defining a fluid inlet at one end of the cylinder, means defining a fluid outlet at the other end of the cylinder, a piston reciprocable in the cylinder formed with a restricted opening therein for flow of fluid from the inlet to the outlet, means biasing the piston toward the inlet end of the cylinder, means defining a plurality of metering ports in the wall of the cylinder adapted to be concurrently and progressively opened by the piston by movement thereof away from the inlet end of the cylinder,

a set of fluid discharge connections in the body, and duct means connecting each said port to a said discharge contraction, one of the fluid discharge connections being at the same end of the body as the said fluid outlet.

8. A fuel system tor but not including a gas turbine engine or "the like having small flow and large flow fucl inlets, the system comprising, in combination, a body defining a cylinder, means defining a fluid inlet at one end of the cylinder, means defining a first fluid outlet at the other end of the cylinder, a piston reciprocable in the cylinder formed with a restricted opening therein for flow of fluid from the inlet to the outlet, means biasing the piston towardthe inlet end of the cylinder, means defining a metering port in the wall of the'cylinder adapted to be progressively opened by the piston by movement thereof away from the inlet end of the cylinder, means for connecting the first fluid outlet to at least one small flow fuel inlet of the engine, means for connecting the metering port to at least :one large flow fuel inlet of the engine, and means for supplying fuel at a regulated rate to the inlet of the cylinder.

9. A fuel system for but not including a gas turbine engine or the like having small flow and large flow fuel inlets, the system comprising, in combination, a body defining a cylinder, means defining a fluid inlet at one end of the cylinder, means defining a first fluid outlet at the other end of the cylinder, a piston reciprocable in the cylinden formed with a restricted opening therein for flow of fluid from the inlet to the outlet, means biasing the piston toward the inlet end of the cylinder, means defining a plurality of metering ports in the wall of the cylinder adapted to be concurrently and progressively opened by the piston by movement thereof away from the inlet end of the cylinder, means for connecting the first fluid outlet to small flow fuel inlets of the engine, means for connecting each metering port individually to a large flow fuel inlet of the engine, and means for supplying fuel at a regulated rate to the inlet of the cylinder.

10. A flow divider as recited in claim 1 in which the metering port is so located'with respect to the inlet end of the cylinder that the piston has an initial range of idle movement before it begins'to open the metering port.

11. A flow divider as recited in claim 2 in which the metering ports are :so located with respect to the inlet end of the cylinder that the piston has an initial range of idle movement before it begins to open the metering ports.

12. A fuel system as recited in claim 8 in which the metering port is so located with respect to the inlet end of the cylinder that the piston has an initial range of idle movement before it begins to open the metering port.

l3. A .fuel system as recited in claim 9 in which the metering ports are so located with respect to the inlet end cf the cylinder that the piston has an initial range of idle movement before it begins to open the metering ports.

l4. A flow divider comprising, in combination, a cylindcr, a piston freely reciprocable therein and provided with a restricted fluid passage between the faces thereof, a fluid inlet at one end of the cylinder, 21 first fluid outlet at theothcr end of the cylinder, resilient means biasing the piston toward the inlet end of the cylinder, 21 fluid metering port formed in the wall of the cylinder, the metering port being connected to a second fluid outlet, the port being located so as to be closed by the piston in its normal biased position at the inlet end of the cylinder and to be opened by the piston after an initial range of idle movement from the normal position; the resilient means comprising a first means offering relatively light resistance to movement of the piston through a substantial part of the idle range and a second means offering relatively heavy resistance to further movement, and a static pressure connection extending from the cylinder at the outlet side of the piston to an external connection on the body.

References Cited in the file of this patent UNITED STATES PATENTS 1,903,332 Bellar Apr. 4, 1933 2,027,360 Alden Jan. 14, 1936 2,073,072 Pontow Mar. 9, 1937 2,430,264 Wicgland et al Nov, 4, 1947 2,476,701 Cochrane July 19, 1949 2,500,627 Chinn Mar. 14, 1950 FOREIGN PATENTS 577,132 Great Britain May 7, 1946 

